1. Field of the Invention
The present invention generally relates to a technique for generating an image bokeh effect.
2. Description of Related Art
In photography, “bokeh” is a blur effect produced in an out-of-focus part of an image by a lens in order to enhance an aesthetic quality and emphasize a primary subject.
General speaking, a camera lens may only produce a fairly limited blur effect. To attain a satisfactory blur effect, conditions such as large aperture and long focal distance must be satisfied. In other words, a wide-aperture lens is required to enhance the blurriness of a long-distance object to create a blur effect so that a primary subject may stand out from a background. However, due to gigantic volume and expensive cost, a wide-aperture lens is not normally equipped in a consumer camera. In the related prior arts for generating an image bokeh effect, an image is mainly divided into a foreground region and a background region, where a blurring process is performed on the background region by using a blur filter. A more advanced approach is to set a different blur level according to a distance between each pixel of the image and a focal plane.
Nevertheless, optical properties of an image capturing device are often neglected in the prior arts. For example, an optical aberration is a departure of an actual image and an ideal image due to refraction, which causes a circle of confusion varying in different intensity distributions and sizes. The so-called “circle of confusion” is a diffused circle caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. That is, an intensity distribution and a size of a circle of confusion may differ based on a relative position and distance from a focal plane. Hence, in the prior arts, a natural bokeh effect may not be simulated since only one single blur filter is used.